For the weld repair of nuclear related structures, friction stir welding (FSW) is being developed as a technique for repair of irradiated materials without helium induced cracking. The mitigation of helium induced cracking in the welded joint heat affected zone (HAZ), a transition metallurgical zone between the weld zone and base metal, during repair welding is a great challenge in nuclear industry. Traditional fusion welding technologies applied to weld repair of irradiated materials is limited to helium levels as low as a couple of atomic parts per million (appm), that may be surpassed in reactor materials under extended plant operating lifetimes. FSW is a solid-state joining technology that reduces the drivers (temperature and residual stress) for helium-induced cracking. This paper will detail the FSW procedure developed first with un-irradiated 304L stainless steel (304L SS) coupons and then transferred to the FSW located in a specially designed welding facility located at a hot cell at the Oak Ridge National Laboratory. The successful early results of FSW of an irradiated 304L SS coupon containing 26 appm helium are discussed. Helium induced cracking was not observed by scanning electron microscopy in weld zone and FSW metallurgical zones between the weld zone and base metal, i.e. thermal mechanical affected zone (TMAZ) and HAZ. Characterization of the weld, TMAZ and HAZ regions will be detailed in this paper.